Add gfx memory controller support for van gogh.

v2: don't use dynamic invalidate eng allocation for van gogh.
v3: squash in other fixes
v4: rebase
Signed-off-by: Huang Rui <ray.huang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>